Magnetic storage systems typically store information on a magnetic storage material, such as a magnetic disk, by controlling the direction of a magnetic field on a portion of the disk associated with a given bit. For example, a magnetic field in a first direction can indicate a first binary value, such as a binary value of zero, while a magnetic field in the opposite direction indicates a second binary value, such as a binary value of one. Generally, the direction of the magnetic field is controlled by controlling the direction of current through an inductive write head in order to change the magnetic domains on the magnetic storage material.
The electromotive force caused by the self inductance of the write head must be overcome. Typically, the self inductance of the write head is overcome using a large current spike, referred to as a “pre-charge,” at the beginning of the write cycle. The resulting voltage spike, generally given by the value of the inductance multiplied by the change in current per unit of time, has a finite rise time due to the inductance. Thus, the magnitude of the voltage spike varies in proportion to the change in current per unit of time (i.e., the faster the current change, the larger the voltage spike). The resulting voltage spikes create large traveling waves and overshoot on the current waveforms which travel down the transmission line, reflect back off of the write head and cause unwanted changes to the write current waveforms.
A need therefore exists for a method and apparatus for changing the magnetic domains of a magnetic storage system that mitigates these above-described issues and is useful for high performance magnetic storage systems. A further need exists for techniques for reducing voltage spikes in such magnetic storage systems.